Photographs, transparencies, documents and other images are often electronically scanned to produce a digital representation of the image. Typically, the image is scanned with light in order to generate a digital representation of the image.
In image scanning devices, one or more light-emitting devices are used as the exposure lamp for purposes of scanning. In many desktop scanners, one or more cold cathode fluorescent lamps (CCFLs) are employed. CCFLs have many advantages over other types of light sources, including high intensity, long life, price and high efficiency. However, compared to other light sources, CCFLs require a longer period of time to warm-up. Typically, a CCFL may take from ten seconds to over sixty seconds to approach maximum light output. As such, waiting for a CCFL to become fully warmed-up can delay scanning, particularly when scanner calibration is to be performed prior to the first scan following activation (i.e., initial powering on or resuming from suspend or sleep mode) of the lamp.
Scanner calibration is a well-established process directed to reducing the defects resulting from illumination and sensor array sensitivity non-uniformity. Typically, a scanner is calibrated to a surface of known color (e.g., a white surface), often referred to as a calibration strip. The calibration strip is scanned, and the response signals from the sensors in the scanner are analyzed. Since the calibration strip is a known color, the calibration scan may be used to determine the spectral characteristics (e.g., color) and intensity of light emitted from the lamp, and compute an appropriate gain to be used during subsequent scanning. Such calibration is necessary since, among other things, the spectral characteristics and intensity of emitted light will change over the life of the lamp. In most scanners, however, calibration is not performed until the lamp is fully warmed-up, thus further delaying the first scan following lamp activation.